Various types of radiation detection technologies are employed in radiation portal monitoring systems for screening and discovering illicit special nuclear material (SNM) in cargo by detecting neutrons and/or gamma-rays emitted by SNM, whether emitted spontaneously or induced with active interrogating beams.
For example, large organic plastic or liquid scintillators are commonly used in radiation portal monitors. While these devices have a relatively poor spectral response, they often rely on rate-based approaches, i.e. detecting an increase in the rate of incoming particles compared to background, which have been shown to be effective for detection. However, plastic organic scintillators are expensive to build in large volumes to approach 4π solid angle coverage of a cargo container and so are unlikely to be sensitive to neutron multiplicity. And liquid scintillators are often toxic and highly flammable. Ease of operation in the field and environmental/physical safety are important considerations of radiation portal monitoring operations. Most current radiation detectors however use materials that are either expensive, hazardous, or need to be operated at cryogenic temperatures.
There is therefore a need for a radiation detector technology capable of use in radiation portal monitoring that is simple, cost effective (thus highly scalable to large volumes) and safe, i.e. environmentally benign.